During 2016 to 2017, the Great Barrier Reef experienced an unprecedented back-to-back bleaching event. In 2016, more than 60 percent of the corals of the reef’s northern section experienced bleaching. Ultimately, roughly 2/3 of the shallow water corals along this section of the reef perished.

In 2017, warmer than normal waters shifted south. As a result, the central section of the Great Barrier Reef is presently experiencing 60 percent or higher bleaching rates. Now, mass mortality in regions unaffected or minimally affected by last year’s record bleaching is expected.

In other words, back-to-back torrents of warm water are walking from north-to-south down the reef, taking out corals as they go from year-to-year, like some merciless ocean blow-torch. And what’s happening is that ocean temperatures are now entering a range where this kind of heat-caused mortality event is becoming more and more likely to occur at frequent intervals.

“The significance of bleaching this year is that it’s back to back, so there’s been zero time for recovery. It’s too early yet to tell what the full death toll will be from this year’s bleaching, but clearly it will extend 500km south of last year’s bleaching.”

Reefs require from 10 to 15 years to recover from the effects of severe bleaching and mortality. They can only bounce back if nearby live corals that survived can regrow into previously denuded sections. But the back-to-back waves of annual heat are ruining that needed connectivity even as the warming ocean is slamming the window shut on the required respite periods.

(The Great Barrier Reef is now experiencing the fastest rate of ocean warming since it began to form about 20 million years ago. Image source: Australia’s Bureau of Meteorology.)

David Sugget, University of Technology Sydney’s lead reef researcher, notes:

“It’s that connection ultimately that will drive the rate and extent of recovery. So if bleaching events are moving around the [Great Barrier Reef] system on an annual basis, it does really undermine any potential resilience through connectivity between neighbouring reefs.”

Since 1900, sea surface temperatures in the region of the Great Barrier Reef during times when the reef is most vulnerable to bleaching — late austral summer and early austral autumn — have risen by 1.5 to 2 degrees Celsius. And the rate of rise during recent years is accelerating. The result is that the risk of multiple severe bleaching events hitting the reef within decadal timescales is now high. And the reef is likely to continue to receive multiple blows as bad or worse than those experienced in the 2016-2017 timeframe.

Some Australian politicians are now promising new laws to help reduce runoff that also stresses the reef. But these policies do not address the root cause of what is now a threat to the reef’s very existence. The bleaching that is killing the reef is caused by ocean warming. And that warming, in its turn, is caused by fossil fuel burning which dumps billions of tons of heat-trapping gasses into the atmosphere each year. According to reports from NOAA, the rate of greenhouse gas accumulation is presently 100 to 200 times faster than at the end of the last ice age. And if this rate of greenhouse gas accumulation continues, there is no chance that the Great Barrier Reef, and most of the other reefs of the world, will survive.

On March 2nd, 2017, the Great Barrier Reef was already starting to show signs of bleaching. After suffering a worst-ever coral bleaching event in 2016, concerns were high that warmer waters could again strike the reef — spurring a second consecutive mass die-off. Even worse, some scientists were concerned that 2017’s bleaching could exceed the intensity of the record 2016 event.

Now it appears that just such a catastrophe is underway. And scientists expect about 2/3 of the world’s largest reef to experience bleaching over the next couple of months.

According to reports from Eyewitness News in Australia — the Great Barrier Reef has been given a “terminal prognosis” by scientists unless the rate of global warming is slowed. The March 10 news report noted that “one of the world’s greatest natural treasures is losing its fight for life” as a second mass coral bleaching event impacts the reef in as many years. Richard Leck of the World Wildlife Fund expressed his shock stating “No scientists ever thought that we would have back-to-back mass coral bleaching events… This is climate change in your face.”

Unfortunately for the reef and for the rest of world’s natural wonders, coastlines, biological diversity, cities and nations, the rate of global warming appears to be accelerating. A situation that will put most of life on Earth, including its corals and the crops human beings rely on for food, into a state of permanent heat stress.

(Fourth consecutive record hot year in a row? If it happens, it would be just one more unprecedented, unexpected event related to climate change to add to the a long and growing list. Image source: Zeke Hausfather.)

We should note that such an occurrence would be very odd — flying in the face of traditional understanding of the El Nino/La Nina cycle. Usually, post El Nino years tend to cool somewhat (including the effect of follow-on La Nina events) even as the overall global warming trend has ramped higher. So if we do experience a record warm year post La Nina, then other factors are helping to drive the global climate system. And the chief suspects at this time appear to be positive Pacific Decadal Oscillation, a Polar Amplification associated with global warming, and spiking ocean temperatures associated with global warming.

Conditions in Context — Climate Tipping Points

To be very clear, what’s happening to the Great Barrier Reef at this time is terrible. But it is not an isolated event. Regions the world over are starting to feel increasingly worsening impacts from climate change. To name just a few of the major impacts now rippling across the globe: Parts of East Africa are getting pushed toward lower farm productivity and ultimate uninhabitability by the rising heat, Northern Hemisphere summer sea ice now has an expected lifespan of 1 to 15 years, growing seasons around the world are under assault from the rising temperatures, coastal cities are in peril from rising waters, and Antarctic and Greenland glaciers are lurching toward the sea.

(A graphic of potential climate tipping points produced by the University of East Anglia. We should probably now also add East Antarctic Ice Sheet, East Africa drought, and expanding ocean dead zones to the list. It’s worth noting that these identified climate tipping points included a degree of uncertainty — meaning that temperature levels needed to set off these events weren’t fully nailed down, nor were the timeframes under which such potential scenarios were likely to occur. But it was generally assumed that crossing any of these tipping points would result in very harmful and wide-ranging impacts. To this point, it appears that we are in the process of crossing the coral bleaching, Arctic sea ice loss, increasing crop stress, expanding ocean dead zones, increasing global wildfires, worsening floods and droughts, and glacial destabilization tipping points at this time.)

All these events are happening with the world at 1.2 C hotter than 1880s averages and warming at what appears to be a rather swift rate. So we appear to be at a threshold now where dangerous and very harmful climate events are starting to occur. In other words, we’re starting to cross some of the forewarned climate tipping points. And these events can arise quite suddenly to produce wide-ranging impacts to human populations and the biodiversity of life on Earth.

The imperative to act by cutting human fossil fuel emissions as rapidly as possible couldn’t be more obvious or urgent. And as part of that imperative, it appears that the removal of fossil fuel backing politicians (like Trump, Scott Pruitt, James Inhoffe and other climate change denying republicans in the US) will be necessary to achieve any kind of rational response to this very real threat to pretty much everyone and everything living on Earth.

During early 2017, the region over Australia’s Great Barrier Reef (GBR) experienced its hottest summer atmospheric temperatures on record. Peak water temperatures lag peak air temperatures by about a month. But already, sections of one of the world’s most vital marine sanctuaries are experiencing bleaching and disease. Worryingly, bleaching and heat stress is expanding over the reef at a faster rate than at the same time last year.

(The Great Barrier Reef is already experiencing extensive bleaching in 2017. With warmer waters headed toward the reef over the coming weeks, researchers fear that this year’s coral mortality event could match or exceed 2016’s severe damage and loss. Image source: Commons.)

A Precious Global Treasure Under Threat

During 2016, the GBR experienced its worst coral bleaching event on record. This severe event followed two years (2014-2015) in which the reef saw less widespread bleaching. A strong El Nino combined with the highest global temperatures ever measured to produce ocean conditions that were too hot to support living corals and many regions saw bleaching and high mortality. In the reef’s northern sections, more than 2/3 of the corals bleached and died out.

(Under human-forced warming the frequency of coral bleaching events and reef mortality is expected to dramatically increase over the coming decades. However, with global temperatures now 1.2 C warmer than 1880s levels, the amount of stress to corals is already remarkably high. Image source: The World Resources Institute.)

Nearer-term concerns were also raised that risks to the reef remained high in the present abnormally warm ocean environment. For as 2017 followed 2016, the global coral bleaching event that began in 2014, and that had already claimed the lives of so many of the world’s corals, remained in force.

During the winter of 2016-2017, a weak La Nina event (NOAA) brought some hope that the GBR might get a chance to recover from this most recent spate of extreme ocean warmth. However, by February, La Nina (which was never strong enough to be officially recorded by Australia’s BoM) had faded even as indicators pointed toward a new El Nino beginning to gather. Meanwhile, global atmospheric carbon continued to increase — hitting 490 CO2e by late 2016.

(NOAA predicts another bad year for the world’s corals as a new El Nino threatens to emerge and as global temperatures remain near record highs set in 2016. Image source: NOAA.)

“Queensland has just experienced its hottest summer on record and above average temperatures are predicted until the end of March. Some corals were still under stress from last year’s bleaching event and that was exacerbated by a warmer than average winter. The next four weeks will be critical and we can only hope that water temperatures will be cooler than the forecast.’’

The six reefs in question, stretching from Cairns to Townsville, already showed 60 percent bleaching — primarily among the more heat-sensitive corals. And the extent of bleaching was more advanced than during the same time in 2016. Over the coming weeks, the pulse of warm water is expected to spread, putting still more corals at risk as the unprecedented ocean heat moves southward through the marine sanctuary.

So it appears that the GBR is in for another rough summer — one with the potential to see impacts similar to or exceeding those of 2016. Moreover, with global oceans continuing to warm, with world governments still dragging heels on carbon emissions reductions, and with Trump and others vowing to reinvigorate coal, the plight of the GBR is now quite dire.

(A global coral bleaching event that began in 2014 continues. It is the longest coral bleaching event on record. But unless oceans somehow cool off, it won’t really end. With only a weak La Nina emerging following a strong El Nino and a record spike in global temperatures, there is some risk that this ongoing event will ebb and flare on a nearly indefinite basis. Continued fossil fuel burning, meanwhile, will continue to add heat to the global climate system — presenting worsening medium and long term bleaching pressure for corals. Image source: Coral Reef Watch.)

The Worst Global Coral Bleaching Event Ever Recorded…

This new record spike in global surface temperatures set off the worst coral bleaching event ever recorded. Around the world, reef systems came under severe stress as sea surface and near surface temperatures exceeded 28-30 degrees Celsius.

Among the hardest hit regions were the reefs of Kiribati. There, sea surface temperatures hit up to 31.4 C on an extended basis. Such hot waters are now expected to have wiped out all but 1 to 5 percent of Kiribati’s living corals. So, for all practical purposes, the reefs of that island republic have been wiped out.

(A weak La Nina has probably already cooled ocean surfaces as much as they will be cooled during 2016 and 2017. But despite this cooling, ocean near-surface waters are still too hot for corals in many places. Relative, if mild, ocean surface warming should occur as ENSO is predicted to shift into neutral status. If coral bleaching is ongoing through La Nina, then it is unlikely to cease as the global ocean starts to warm again. Global sea surface temperature anomaly image source: Earth Nullschool.)

In Australia, the Great Barrier Reef (GBR) also saw its worst bleaching event on record. There, 93 percent of corals are reported to have experienced bleaching. Meanwhile, about 50 percent of corals have died in the northern section of the GBR. In the media, a controversy has raged over whether or not this event is the start of the great reef’s swansong. To be clear, the GBR was not killed off by the most recent large bleaching event. But it was dealt a very severe blow. With the world continuing to warm as fossil fuel burning remains ongoing, a similar blow could occur as soon as the next El Nino or the one after. And the story for many of the world’s remaining reefs could well be the same.

The austral summer is expected to bring bleaching over far-flung regions encircling the southern part of the globe. Thankfully, most of the GBR is only under a bleaching watch for now. But bleaching warnings and alerts abound and, unfortunately, many reefs are likely to see continued die-offs even after El Nino has long since faded.

… And May Just, For all Practical Purposes, Continue

As the current La Nina is rather weak, and as it is predicted to shallow into an ENSO neutral state by spring, it appears that sea surface temperatures may be in the process of bottoming out. Global fossil fuel emissions, meanwhile, continue to add heat to the ocean system. As a result, the coral bleaching pressure that we are seeing during the period of November 2016 through February of 2017, unless we see a resurgence to a stronger La Nina event over the next year or two, could be the minimum we will see over the coming years. And if that is the case, then the coral bleaching event that hasn’t ended for the past two years may not really end at all.

It’s a hard, tough thing to consider. One of those possibilities people justifiably do not want to talk about. This notion that a creature we’re fond of and familiar with — a glorious living being along with all its near and distant relatives — could be entirely removed from the web of existence here on Earth.

Our aversion to the topic likely stems from our own fear of death. Or worse — the notion that the entire human race might eventually be faced with such an end. But extinction is a threat that we’ll see arising more and more as we force the world to rapidly warm. For species of the world now face existential crisis with increasing frequency as atmospheric and ocean temperatures have risen so fast that a growing number of them have simply become unable to cope with the heat.

The damage comes in the form of extreme ocean heat. Heat resulting from global temperatures that are now well in excess of 1 degree C above preindustrial times. Heat that has forced ocean temperature variability into a range that is now lethal for certain forms of sea life. Particularly for the world’s corals which are now suffering and dying through the worst global bleaching event ever experienced.

The Worst Global Coral Bleaching Event Ever Experienced

During 2014 the oceans began to heat up into never-before seen temperature ranges. This warming initiated a global coral bleaching event that worsened throughout 2015. By early 2016 global surface temperatures rocketed to about 1.5 C above 1880s averages for the months of February and March. These new record high temperatures came on the back of annual carbon emissions now in the range of 13 billion tons each year and at the hotter end of the global natural variability cycle called El Nino. Both the atmosphere near the land surface and the upper levels of the ocean experienced this extreme warming.

In the ocean, corals rely on symbiotic microbes to aid in the production of energy for their cellular bodies. These microbes are what give the corals their wild arrays of varied and brilliant colors. But if water temperatures rise high enough, the symbiotic microbes that the corals rely on begin to produce substances that are toxic to the corals. At this point, the corals expel the microbes and lose their brilliant coloration — reverting to a stark white.

(A vast region of the world’s ocean system continues to experience coral bleaching. In area, extent, height of extreme temperature, and duration, the current global coral bleaching event is the worst ever experienced by a good margin. As global temperatures continue to warm due to ongoing fossil fuel burning and related carbon emissions, widespread coral bleaching is likely to become an annual occurrence. Temperatures have risen far enough and will continue to rise for long enough to set about ocean conditions that will result in mass coral die-offs around the world. Image source: NOAA.)

Bleaching isn’t necessarily lethal to corals. However, once the microbes are gone, the corals have lost a key energy source and will eventually die without them. If ocean temperatures return to normal soon enough, the corals can begin to accept the symbiotic microbes back, return to a healthy cellular energy production, and survive — albeit in a weakened and more vulnerable state for some time to come. But if ocean temperatures remain too warm for an extended period, then the corals will be deprived of energy and nutrients for too long and they will inevitably perish.

The kind of coral bleaching event that we’re experiencing now is a mass killer of corals. Not simply due to the heat itself, but due to the long duration of the extreme temperature spike. By late February, many ocean scientists were very concerned about the already severe damage reports that were starting to come in. At that time, NOAA issued this warning:

“We are currently experiencing the longest global coral bleaching event ever observed. We may be looking at a 2- to 2½-year-long event. Some areas have already seen bleaching two years in a row.”

93 Percent of Great Barrier Reef Affected by Bleaching

By late February, the level of concern for the Great Barrier Reef was palpable. Stark reports were starting to come in from places like Fiji — which had experienced two years of severe bleaching — and Christmas Atoll about 1,300 miles south of Hawaii — whose reported losses were best described as staggering. So far, the worst of the hot water had stayed away from Australia’s great reef.

But by early March a plume of very extreme ocean heat began to appear over The Great Barrier Reef’s northern sections. Sea surface temperatures spiked to well above, a dangerous to corals, 30 degrees Celsius for days and weeks. This 30 C or greater heat extended deep — hitting as far as 50 meters below the ocean surface over the reef. And it rippled southward — hitting section after section until few parts of the reef were spared.

“Tragically, this is the most remote part of the Reef, and its remoteness has protected it from most human pressures: but not climate change. North of Port Douglas, we’re already measuring an average of close to 50% mortality of bleached corals. At some reefs, the final death toll is likely to exceed 90%. When bleaching is this severe it affects almost all coral species, including old, slow-growing corals that once lost will take decades or longer to return (Emphasis added).”

But with the oceans still warming, and with more and still worse coral bleaching events almost certainly on the way, the question has to be asked — will these corals ever be afforded the opportunity to recover?

When ocean surface temperatures warm into a range of 2 C above 1880s levels — the kind of severe global heating that could arise under worst-case fossil fuel emissions and related warming scenarios by the mid 2030s — corals in the Great Barrier Reef are expected to experience bleaching on an annual basis. Every year, in other words, would be a mass coral bleaching and die-off year.

(Sea surface temperatures and temperatures withing the top 50 meters of water over the Great Barrier Reef of Australia rose to 3-4 C above average during the austral Summer and Fall of 2016. These record temperatures lasted for weeks in some regions setting off the worst coral bleaching event the Great Barrier Reef has ever seen. By mid-Century, coral bleaching and mass die-offs are likely to occur on an annual basis as global temperatures surpass the 1.5 C and 2 C thresholds. Image source: Earth Nullschool.)

Globally, bleaching events under even moderate fossil fuel emissions scenarios would tend to take up much of the Equatorial region on an annual basis by mid-Century. Events that can, during single years, wipe out between 90 and 95 percent of corals at any given location. A handful of corals will likely survive these events — representing a remote and far-flung remnant who were simply a bit hardier, or lucky, or who had developed an ability to accept microbes that are tolerant to warmer temperatures. But these hardy or fortunate few would take hundreds to thousands of years to re-establish previous coral reef vitality even if other harmful ocean conditions did not arrive to provide still more damage.

As coral bleaching expands at the Equator due to increasing rates of ocean warming, increasing levels of carbon dioxide in the atmosphere causes oceans to become more acidic. Cooler waters at the poles are better able to transfer gasses into the ocean’s waters. And higher levels of carbon dioxide in the world ocean results in a growing acidity that is harmful to corals. Increasing levels of ocean acidity thus creep down from the poles at the same time that bleaching events move up from the Equator.

If fossil fuel emissions continue, by mid-Century atmospheric carbon dioxide levels in the range of 450 to 500 parts per million will have provided a never-before seen spike to ocean acidity. Such high ocean acidity would then provide a second severe blow to corals already devastated by bleaching events. It’s a 1-2 punch that represents a mass extinction threat for corals this Century. And we’re starting to see the severe impacts ramp up now.

(Coral bleaching is a severe threat to tropical coral reefs now. But CO2 potentially hitting above 500 parts per million, according to a 2014 study, risks a complete loss of equatorial coral reefs by 2050 to 2100. Between bleaching and acidification, there’s no way out for corals so long as fossil fuel burning continues. Image source: Threat to Coral Reefs From Ocean Acidification.)

The only hope for stopping this ever-expanding harm is a rapid cessation of fossil fuel emissions. And we owe it to the corals of the world, the millions of species that depend on them, and the hundreds of millions of people whose food sources and economic well being come from the corals.

“And Then We Wept”

When researchers told students of the extent of harm to corals upon the Great Barrier Reef, the students were reported to have wept. And with good reason. For our Earth had just experienced a profound death of beauty. A death of a vital and wondrous living treasure of our world. A priceless liquid gem of our Earth. A wonder that gives life to millions of species and one that grants both food and vitality to Australia herself. For if the reef goes, so does a huge portion of the living wealth of that Nation and our world.

Sadly, the tears will just keep coming and coming as these kinds of events are bound to worsen without the most dramatic and urgent global actions. The current and most recent catastrophe is thus yet one more in a litany of wake up calls to the world. But will we hear it loud and clear enough to act in ways that are necessary to ensure the corals survival? And what of the billions of creatures and of the millions of humans too that depend on the corals? Do we care about them enough to act?

(Please support public, non-special interest based science like the essential work that has been provided by Terry Hughes over so many years and decades. Scientists like Terry provide a vital public service. For years, they have given us a clear warning of a very real and ever more present danger. A warning that gives us a fleeting opportunity to respond to events before we lose the richest living treasures of our world. Before we are bereft of our ability to continue to make livelihoods as environmental abundance and the related regional and global life support systems are irreparably damaged.)